1. Field of the Invention
The present invention relates to low viscosity white graft polymer dispersions in polyoxyalkylene polyether polyols and flame retardant polyurethane foams prepared therefrom. More particularly, the invention relates to graft polymer dispersions prepared by the improved process employing free radical polymerization of an ethylenically unsaturated monomer or mixture of monomers in a polyol mixture containing less than 0.1 mole of induced unsaturation per mole of polyol mixture. This improved process yields stable, non-settling dispersions with graft polymer contents of 30 percent by weight and higher employing monomer mixtures which contain more than about 55 percent by weight styrene as the comonomer. Further, the invention relates to an improved process employing free radical polymerization in a polyetherester polyol-polyoxyalkylene polyether polyol mixture containing less tha 0.1 mole of induced unsaturation per mole of polyol mixture wherein the unsaturated moiety is an isomerized maleate containing polyetherester polyol. Even more particularly the invention relates to an improved process employing free radical polymerization in a polyol mixture containing polyetherester polyol-polyoxyalkylene polyether polyol mixture which was prepared by reacting a polyoxyalkylene polyether polyol, a polycarboxylic acid anhydride and an alkylene oxide in the presence of an effective amount of a catalyst selected from the group consisting of salts and oxides of divalent metals.
2. Description of the Prior Art
The prior art, as evidenced by U.S. Pat. Nos. 3,652,658; 3,875,258; 3,950,317, and Reissue Pat. Nos. 28,715 and 29,014 teaches the preparation of graft polymer dispersions which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in the presence of polyols. The above patents disclose various methods of preparing graft polymer dispersions. U.S. Pat. No. 3,931,092 teaches the preparation of polymeric solids by polymerizing in the presence of a free-radical initiator and an organic solvent. The solvent concentration employed is from about 1 part to 19 parts by weight per part of the hydroxy-terminated organic compound which has a polymerizable carbon double bond. U.S. Pat. No. 3,953,393 teaches the preparation of graft copolymer dispersions by employing alkylmercaptan chain transferring agents at concentrations from 0.1 to 2 percent by weight based on the weight of vinyl monomer.
Stable dispersions of polymers in polyols have found broad commercial use in the preparation of polyurethanes. The use of these dispersions, known in the trade as graft or polymer polyols, improves processing and, among other properties, the firmness of the polyurethane products, often expressed as load bearing or modulus. There have been many attempts to improve the products representing the present state of the art. Efforts have been directed towards increasing the amount of polymer which is dispersed in the polyol, the obvious benefit being that firmer polyurethanes can be produced. Two major obstacles have been found: the viscosities of the resulting dispersions were too high and/or relatively high levels of acrylonitrile had to be used in the monomer mixtures employed.
The use of high levels (.gtoreq.50 percent by weight) of acrylonitrile and, correspondingly, relatively low levels of the most common comonomer, styrene (.ltoreq.50 percent) had two very undesirable effects. The resulting dispersions are tan to brown in color with a strong tendency to turn even darker in color during the highly exothermic polyurethane foam formation giving, for example, slab foams with a strong tendency to scorch. But even more undesirable, polyurethane foams made from these products cannot be satisfactorily flame retarded to pass flammability tests which are standard in the industry.
As mentioned before, there have been attempts to prepare high polymer (.gtoreq.30 percent) containing dispersions with acceptable viscosities. These products contain ratios of acrylonitrile to styrene of &gt;50/50 and are tan colored. None of the prior art teaches that polymer dispersions in unsaturated polyols containing less than 0.1 mole of induced unsaturation per mole of polyol mixture may be employed for flame-retardant polyurethane foams. Neither has the prior art taught that in situ free radical polymerizations may be conducted in a polyetherester polyol-polyoxyalkylene polyether polyol mixture containing less than 0.1 mole of induced unsaturation per mole of polyol mixture wherein the unsaturated moiety is an isomerized maleate containing polyetherester polyol. Also, the prior art is silent on the preparation of polyetherester polyols, by the reaction of a polyoxyalkylene polyether polyol, a polycarboxylic acid anhydride, and an alkylene oxide, in the presence of a catalyst selected from the group consisting of salts and oxides of divalent metals.